Liquid cooled circuit device and a manufacturing method thereof

ABSTRACT

A liquid-cooled circuit device including: a module having a circuit element and a module base plate on surface of which the circuit element is mounted; a circuit case for accommodating the module; and a cooling liquid chamber for flowing a cooling liquid in contact with a back face of the module base plate of said module. The module base plate of the module is fitted into an opening provided in a member forming the cooling liquid chamber and welded without a gap.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 10/099,995, filedMar. 19, 2002, the subject matter of which is incorporated by referenceherein.

BACKGROUND OF THE INVENTION

The present invention relates to a liquid-cooled circuit devicecomprising a module of which circuit elements are mounted on a modulebase plate and in which the module is cooled by cooling liquid, and amethod for manufacturing the liquid-cooled circuit device.

In an electronic circuit device having a power circuit element whoseheat emission is high, such as an inverter device for controlling adriving motor of an electric vehicle, liquid cooling using a liquidhaving a greater thermal capacity is effective from the need toefficiently carry out cooling of the power circuit element. For priorart liquid cooling of a power circuit element, a direct heat transfersystem by which a power circuit element is directly immersed in anelectrically insulating cooling liquid and an indirect heat transfersystem by which a circulating cooling liquid is brought into contactwith a circuit case in which a power circuit element is mounted and thepower circuit element is cooled by cooling the circuit case are mainlyused.

However, the direct heat transfer system has a disadvantage of involvingmany incidental problems regarding leak, disposal and safety of specialcooling liquid that is used. In the indirect heat transfer system, whenthe power circuit element is mounted in the circuit case, grease or thelike has to be inserted between them to ensure heat transfer, and thisleads to a disadvantage of poor cooling efficiency because the insertedsubstance obstructs heat radiation of the power circuit element.

As a way to obviate this disadvantage of the indirect heat transfersystem, it is readily conceivable to mount the power circuit element ona base plate (hereinafter a device on which a power circuit element ismounted shall be referred to as a power module) and to bring the coolingliquid into contact with the other face (to be referred to as the backface) of the opposite to that on which the element is mounted, whichwould result in efficient cooling of the power circuit element. In thiscase, it is required to provide an opening in the circuit case and toclose the opening by pressing the back face of the module base plateagainst the opening to bring the cooling liquid into direct contact withthe back face of the module base plate. If there is any gap in thecontacting part of the back face of the module base plate pressedagainst the circuit case opening, the cooling liquid will enter throughthe gap into the circuit case to cause the module and electroniccircuits in the circuit case to be immersed in the cooling liquid andthereby invite erroneous actions by the electronic device.

Then, in order to resolve this problem, a solution is proposed inJP-A-11-163572 specification, according to which the module base plateand the cooling liquid case are joined with screws or the like, and an Oring is provided inside to seal any gap between them, so that even ifthe cooling liquid in the cooling liquid case leaks, the leaked liquidwill not directly enter the circuit case but will be discharged into theatmosphere.

However, the technique described in JP-A-11-163572 specificationrequires a portion on the module base plate for mounting the O ring,screws and so forth, and therefore involves the problem that size of themodule base plate becomes large. Such an enlarged module base plate notonly adds to the cost, because the module base plate itself is ratherexpensive essentially, but also, where a large number of power modulesare to be mounted, the spacing between the power circuit elements wouldbe expanded, resulting in an increased size of the whole device.

In view of these problems of the prior art, an object of the presentinvention is to provide a liquid-cooled circuit device contributing topreventing the module base plate from expanding in size and the coolingliquid from infiltrating into the circuit case, and a manufacturingmethod for such a circuit element device.

BRIEF SUMMARY OF THE INVENTION

A liquid-cooled circuit device according to a first aspect of thepresent invention, comprising: a module comprising a module base plateand a circuit element mounted on the module base plate; a circuit casefor housing the module; a cooling case through which cooling liquidflows, said cooling liquid being in contact with a back face of themodule base plate; and a module supporting having an opening foraccommodating the module base plate therein; wherein said module baseplate is placed into said opening of said module supporting plate, edgesof the opening and the module base plate are joined by welding to eachother without a gap therebetween; said circuit case is formed with anopening smaller than said module supporting plate; said modulesupporting plate is fixed to the circuit case so as to block saidopening in said circuit case from outside the circuit case and to causesaid circuit element of said module mounted on the module supportingplate to be positioned within the circuit case; said cooling case isformed with a recess forming a cooling liquid chamber through which thecooling liquid flows; and said cooling case is fixed to said circuitcase so that said recess faces said module supporting plate.

With the structure described above, the module base plate and the modulesupporting plate can be regarded as an integrated structure by welding,there is no conceivable risk of liquid leakage from between them.Furthermore, since the module supporting plate is greater in size thanthe opening in the circuit case and blocks the opening from outside thecircuit case, even if the cooling liquid leaks from between thesupporting plate and the circuit case, the leaked liquid will bedischarged outside instead of entering the circuit case and soakingcircuit elements, base plates and wiring arranged in the circuit casebecause a connecting portion between them are positioned outside thecircuit case. Further, as the back face of the module base plate facesthe inside of the cooling case from the opening in the module supportingplate, the back face of the module base plate is in direct contact withthe cooling liquid in the cooling case to efficiently cool the module.Moreover, since the module base plate is joined to the module supportingplate by welding, there is no need for the module base plate to beprovided with any O ring for sealing or screws for connection, making iteasier to reduce the size of the module base plate. Furthermore, sincethe module is mounted inside the circuit case, terminal wiring to thecontrol circuit is simplified. To add, while welding usually means amethod of melting the parts to be joined, and has such versions as arcwelding, laser welding, electron beam welding and the like, there aremethods by which the parts to be joined are not melted, such assoldering, brazing, friction stir welding and the like. In presentspecification, “welding” is as a generic term for both categories ofjoining methods. It has to be noted, however, that welding of a modulebase plate on which a circuit element is mounted should preferably beaccomplished by a friction stir welding method to minimize the thermalimpact on the circuit element and other members.

A liquid-cooled circuit device according to a second aspect of theinvention, comprising: a module comprising a module base plate and acircuit element mounted on the module base plate; a circuit case forhousing the module; and a cooling case through which cooling liquidflows, said cooling liquid being in contact with a back face of themodule base plate; wherein said circuit case is formed with an opening;said cooling case is formed with a recess forming a cooling liquidchamber through which said cooling liquid passes; the module base plateis arranged so that the circuit element of the module be positionedinside the circuit case, and joined by welding to either an edge of theopening in said circuit case or an edge of an opening of said recess ofsaid cooling case without a gap therebetween; and said cooling case isfixed to the circuit case so that said recess faces toward said openingin said circuit case.

With the structure described above, the module base plate and the edgeof the opening in the circuit case or the module base plate and the edgeof the opening in the cooling case form a structure integrated bywelding, and accordingly there is no conceivable risk of liquid leakagefrom between them. In other words, the inside of the circuit case towhich the module base plate is fitted is in a completely sealed state.Therefore, there is no risk of cooling liquid leaked from inside thecooling case to enter the circuit case. Also, similar to theliquid-cooled circuit device according to the first aspect of theinvention, the present device can also cool the module efficiently, andmakes it easier to reduce the size of the module base plate.Furthermore, this structure allows the number of parts to be reducedthan the first embodiment of the liquid-cooled circuit device.

A liquid-cooled circuit device according to a third aspect of theinvention, comprising: a module comprising a module base plate and acircuit element mounted on the module base plate; and a circuit case forhousing the module; wherein: the module base plate is placed within saidcircuit case so as to partition inside of the circuit case into twochambers, and is joined to an inner face of the circuit case by weldingwithout a gap therebetween; one of the two chambers formed in saidcircuit case, on the side where the circuit element of the module ispresent, forms a circuit accommodating chamber and the other forms acooling liquid chamber; and said cooling liquid chamber is formed withan inlet and outlet for cooling liquid flowing in contact with a backface of the module base plate of the module.

Also with this structure, in dividing the inside of the circuit case bythe module base plate, it is joined by welding to the inner face of thecircuit case without a gap therebetween, so that the cooling liquid fromone of the two chambers, i.e. the cooling liquid chamber, does not enterthe other chamber, the circuit accommodating chamber. Moreover, thisstructure dispenses with sealing members such as O rings and connectingmembers such as screws, resulting in an even smaller number of parts.

Moreover, in the third embodiment of the liquid-cooled circuit device,if some of the parts forming the cooling liquid chamber among the caseforming parts constituting the circuit case are detachably fixed to therest of the case forming parts, maintenance and other tasks can beaccomplished with greater ease though the number of parts somewhatincreases.

A method for manufacturing a circuit element device to achieve theobject is characterized in that a base plate on which a circuit elementis mounted and other member are joined by a friction stir welding methodutilizing a plastic flow due to friction heat generated by rotation of arotary tool. It is preferable here for the base plate and the othermember to contain the same metallic element.

A circuit element device for achieving the object is characterized inthat a base plate on which a circuit element is mounted and other memberare joined to each other by welding, and crystal grains in parts joinedby welding are smaller than the original crystal grains of therespective members. A liquid-cooled circuit device comprising: a modulehaving a circuit element and a module base plate on surface of which thecircuit element is mounted; a circuit case for accommodating saidmodule; and a cooling liquid chamber for flowing a cooling liquid incontact with a back face of said module base plate of said module,wherein said module base plate of said module is fitted into an openingprovided in a member forming said cooling liquid chamber and weldedwithout a gap.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut out perspective view of an essential part of a firstembodiment of a liquid-cooled circuit device according to the invention;

FIG. 2 is a view of a typical circuit of a power module portion of thefirst embodiment of the liquid-cooled circuit device of the invention;

FIG. 3 is a sectional view of an essential part of a second embodimentof the liquid-cooled circuit device of the invention;

FIG. 4 is a cutout perspective view of an essential part of a thirdembodiment of the liquid-cooled circuit device of the invention;

FIG. 5 is a cutout perspective view of an essential part of a fourthembodiment of the liquid-cooled circuit device of the invention;

FIG. 6 is a cutout perspective view of an essential part of a fifthembodiment of the liquid-cooled circuit device of the invention;

FIG. 7 is a cutout perspective view of an essential part of a sixthembodiment of the liquid-cooled circuit device of the invention;

FIG. 8 is a cutout perspective view of an essential part of the seventhembodiment of the liquid-cooled circuit device of the invention;

FIG. 9 is a cutout perspective view of an essential part of an eighthembodiment of the liquid-cooled circuit device of the invention;

FIG. 10 is a cutout perspective view of an essential part of a ninthembodiment of the liquid-cooled circuit device of the invention;

FIG. 11 is a cutout perspective view of an essential part of a tenthembodiment of the liquid-cooled circuit device of the invention;

FIG. 12 is a cutout perspective view of an essential part of an eleventhembodiment of the liquid-cooled circuit device of the invention; and

FIG. 13 is a view showing a friction stir welding method.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of a liquid-cooled circuit device of the presentinvention will be described hereinafter with reference to accompanyingdrawings.

First, a first embodiment of a liquid-cooled circuit device of theinvention will be described with reference to FIGS. 1 and 2. For thisand all the following embodiments and any variation thereof, the sameconstituent elements will be assigned respectively the same referencenumerals, and duplication of description will be avoided. If any oneembodiment or one variation has a plurality of members of the same kind,the same numeral will be assigned to them, differentiated by differentsmall alphabetical letters suffixed to the numeral.

In FIG. 1, reference numerals 1 a through 1 d denote power circuitelements; 2 a and 2 b, module base plates on which the power circuitelements 1 a and 1 b are mounted, respectively; 3, a module supportingplate to which the module base plates 2 a and 2 b are fixed; 4 a and 4b, welded portions between the power module base plates 2 a and 2 b, andthe module supporting plate 3; 5, a circuit case; 6, an opening providedin the circuit case 5; 7, a cooling case; 8, a sealing member (e.g. an Oring) for sealing a gap between the cooling case 7 and the modulesupporting plate 3; 9, a sealing member (e.g. an O ring) for sealing agap between the circuit case 5 and the module supporting plate; 10 a and10 b, bolts for fastening the circuit case 5, the module supportingplate 3 and the cooling case 7 together; 11, a cooling liquid chamber inthe cooling case 7 for letting a cooling liquid pass; 12, the coolingliquid; 13, the inside of the circuit case 5; 14 a and 14 b, elementmounting faces (front faces) of the module base plates 2 a and 2 b,respectively; and 15 a and 15 b, the other faces (back faces) oppositeto the module mounting faces.

Each of the power circuit elements 1 is provided inside with a powerdevice including an insulated gate bipolar transistor (IGBT), which is aheat generating element. The power circuit element 1 is mounted on, andelectrically insulated from, the element mounting face 14 of the modulebase plate 2 to minimize a thermal resistance between the power circuitelement 1 and the base plate 2. In the present arrangement, electricalinsulation is achieved by adhering a highly heat-conductive material,such as AIN ceramics, onto the element mounting face 14 of the baseplate 2, and the power circuit element 1 is soldered onto an electrodepattern formed over that face to constitute the power module.

The module supporting plate 3 is formed with a plurality of openingsmatching the size of the module base plates 2, and the module baseplates 2 are fitted into the openings. The edges of the openings andouter edges of the module base plates 2 are joined by welding without agap therebetween.

The welding is done by a method known as friction stir welding (FSW). Bythe present method, as illustrated in FIG. 13, a rotary tool, which isturning, is inserted to a prescribed depth between members to be joined,in this case between the edges of openings in the module supportingplate 3 and the external edges of the module base plate s2, and therotary tool, kept turning, is shifted in relative position in adirection of a joint line to plastically fluidize the members to bejointed by friction heat between them so that the members can be joinedto each other with only local heat at a low temperature not higher thanthe melting point of the members to be joined (heating by friction). Thecrystal grains of the portion welded by the method, unlike in thoseresulting from laser beam welding, arc beam welding or the like, aresmaller than the original crystal grains of the welded members. Thiswelding method, as it requires only local heating at relatively lowtemperature, can avoid adverse effects such as mechanical distortion ofthe module base plates, deterioration of insulation and other electricalill effects and the like, namely various adverse effects of heat on thepower modules. This welding method, as it gives rise neither metal vapornor metal powder, has another advantage of being able to avoidcontamination of the power modules in the welding process. In thepresent embodiment of the invention, the module supporting plate 3 andthe module base plates 2 are formed of Al alloy or AlSiC alloy, bothbeing excellent in heat transfer performance and suitable for FSW.

As described above, welding of the plurality of power modules onto themodule supporting plate 3 results in integration of the plurality ofpower modules. The size of the module supporting plate 3 is greater thanthat of the opening 6 of the circuit case 5. The module supporting plate3 is set onto the circuit case 5 from outside the circuit case 5 so thatthe power modules mounted on the plate 3 face the inside 13 from theopening 6 of the circuit case 5. Further, the cooling case 7 is set ontothe module supporting plate 3 on the reverse side to the circuit case 5.The bolts 10 a and 10 b are screwed into the circuit case 5, the modulesupporting plate 3 and the cooling case 7 to be connected and fixed toone another. On the side closer to the power circuit elements than thebolts 10 between respective members are inserted the sealing members 8and 9, such as O rings, all around the circumference of each. In theinside 13 of the circuit case 5, a control circuit for the power module,a power supply circuit therefor and their base plates are housed, thoughnot shown.

In the present embodiment, the plurality of power modules, as shown inFIG. 2, constitute a three-phase inverter circuit. In the drawing,reference letter P denotes a plus D.C. power source; N, a minus D.C.power source; 18 a through 18 f, arms each comprising an IGBT and adiode; 19 a through 19 f, collectors; 20 a through 20 f, emitters; 21 athrough 21 f, gates; and 22 a through 22 f, auxiliary emitters. Thethree-phase inverter circuit is structured by six arms in total. Whereone of the power circuit elements 1 constitutes one of the arms in FIG.2 (any one of 18 a through 18 f), a three-phase inverter is formed bythe welding and mounting of six power modules onto the module supportingplate 3. Where power circuit elements 1 constitute two arms in FIG. 2(for instance 18 a and 18 b), a three-phase inverter is formed by thewelding and mounting of three power modules onto the module supportingplate 3. Obviously, where power circuit elements 1 constitute six armsin FIG. 2 (for instance 18 a through 18 f), a three-phase inverter isformed by the welding and mounting of one power module onto the modulesupporting plate 3. This configuration of a three-phase inverter circuitby a single module supporting plate contributes to the convenience ofuse of the present circuit.

One three-phase inverter circuit controls one three-phase motor. Forthis reason, if a given system requires a plurality of motors, thethree-phase inverter circuits corresponding to the numbers of the motorhave to be mounted in the circuit case 5. Therefore, if, for instance,the power circuit elements 1 constitute one arm in FIG. 2 and areapplied to a system having two motors, twelve circuit elements 1 arerequired to constitute two inverter circuits, i.e. (=6×2) circuits. Thetwelve circuit elements 1 constituting the two inverter circuits may befixed to a single module supporting plate 3 or may be fixed to twomodule supporting plates 3, in each of which with six circuit elements 1constituting one inverter circuit may be fixed. While the foregoingdescription referred to three-phase inverter circuits for drivingthree-phase motors, it is needless to say that a two-phase invertercircuit is used for driving two-phase motors.

In the embodiment described above, when the cooling liquid 12 passesthrough the cooling liquid chamber 11, the back faces 15 of the modulebase plates come into direct contact with the cooling liquid 12.Accordingly, the power circuit elements 1 mounted on the module baseplates 2 can be cooled efficiently. Moreover, because the module baseplates 2 and the module supporting plate 3 are joined by the weldedportions 4, there hardly occurs aging deterioration of these jointportions. Therefore, the possibility for the cooling liquid to passthese welded portions 4 and leak into the circuit case is eliminated notonly at present but also in the further, so that it is possible toobtain high reliability. Further, even if the sealing member 8 arrangedbetween the cooling case 7 and the module supporting plate 3deteriorates over time and allows the cooling liquid 12 to leak, thecooling liquid 12 will merely leak out through a gap 16 between them butnot into the circuit case 5 because the connecting part between them ispositioned outside the circuit case 5. Furthermore, because the modulebase plates 2 are welded to the module supporting plate 3, there is noneed to form fixing portions for O rings or screws or the like in themodule base plates 2, and therefore it is possible to reduce the size ofthe module base plates 2. As a result, it is possible to restrain thecost of the module base plates which is relative expensive, and thespacing between the power circuit elements 1 can be narrowed, making itpossible to reduce the size of the whole device. In addition, whereasthe module base plates 2 are joined to the module supporting plate 3 bywelding with a view to reducing their size, since this welding is FSW asdescribed above, the thermal impacts on the power circuit elements 1during the welding process can be suppressed.

Although FSW is applied to the whole circumference of the module baseplates 2 in the present embodiment, if the rotary tool is subject tointerference with other members and prevented from being arranged in theintended welding position, it is permissible to apply some other way ofwelding, such as arc welding, laser beam welding or electron beamwelding, to the obstructed part alone, which may as well be joined by anon-welding method such as soldering or brazing.

Then, a second embodiment of the liquid-cooled circuit device of thepresent invention will be described with reference to FIG. 3.

While the first embodiment of the invention has one module supportingplate 3 for one circuit case 5, the present second embodiment, which isa variation of the first embodiment, has a plurality of modulesupporting plates 3 for one circuit case 5, and substantially the sameas the first embodiment with respect to other structure.

In the second embodiment, two openings 6 a and 6 b are formed at thebottom of the circuit case 5, and module supporting plates 3 a and 3 band cooling cases 7 and 7 are fixed to the openings 6 a and 6 b,respectively. Cooling liquid chambers 11 a and 11 b in the cooling cases7 and 7 are connected to each other in a position not shown, so that acooling liquid 12 a flowing into one cooling liquid chamber 11 a in adirection normal to the surface of the paper of this drawing flow as acooling liquid 12 b out of the other cooling liquid chamber 11 b. Thus,the two cooling liquid chambers 11 a and 11 b here are connected inseries in relation to a cooling liquid supply source. It is notabsolutely necessary to connect the plurality of cooling liquid chambersin series in relation to the cooling liquid supply source as in thepresent embodiment of the invention, but may be connected in parallel inrelation to the cooling liquid supply source with the cooling efficiencyof and the volume of cooling water used for the power module being dulytaken into consideration.

According to the present embodiment, it is possible to attach and detachpower modules to/from the circuit case 5 separately for each modulesupporting plate. For this reason, if a power module in any one of themodule supporting plates 3 runs into trouble, the module supportingplate 3 on which the power module in trouble is mounted can be replaced,but no other module supporting plate 3 needs to be replaced.

Next a third embodiment of the liquid-cooled circuit device of thepresent invention will he described with reference to FIG. 4.

In a bottom of the circuit case 5 are formed a plurality of openings 6as many as power modules to be mounted and matching in size to themodule base plates 2. In each of the openings 6 is placed a module baseplate 2 mounted with a power circuit element 1, and an outercircumference of the base plate 2 and an inner circumference of thecircuit case opening 6 are welded to each other without a gap betweenthem, and the plurality of power modules are thereby fixed to thecircuit case 5. The cooling case 7 is arranged so as to cover theplurality of openings 6 in the circuit case, and fixed to the circuitcase 5 with bolts 10. Between both members, a sealing member 8, such asan O ring, is inserted all around their joining portions.

In the present structure, when the cooling liquid 12 passes through thecooling liquid chamber 11, the back faces 15 of the module base platesand a portion 5 a of the circuit case are efficiently cooled. Since themodule base plates 2 and the circuit case 5 are fixed to each other bywelding, the quality of their joining portion is not subject todeterioration due to aging. Therefore, there is no possibility for thecooling liquid to pass the welded portions 4 and leak into the circuitcase 5, and high reliability can be obtained. Even if the quality of thesealing member 8 deteriorates over time and allows the cooling liquid toleak, the cooling liquid 12 will merely leak out through a gap 16between the cooling case 7 and the circuit case 5, but never into thecircuit case 5.

Furthermore, as the power modules are welded directly to the circuitcase 5 in the present embodiment, the module supporting plate 3 and someof the sealing members 8 in the first embodiment can be dispensed with,and it is possible to restrain manufacturing cost. Moreover, becauseseal portions to be sealed by sealing members are reduced in number,reliability against cooling liquid leakage can be enhanced. Furthermore,as the portion 5 a of the circuit case 5 is also cooled, if amicrocomputer to be used as a control circuit is mounted in or near thisportion 5 a, it can be cooled, too.

While the module base plates 2 are directly welded to the edges of theopenings 6 in the circuit case 5 in the present embodiment, it is alsopermissible to weld the module base plates 2 to the module supportingplates 3 and weld this module supporting plates 3 to the edges of theopenings 6 in the circuit case 5 as in the first embodiment.

A fourth embodiment of the liquid-cooled circuit device of the presentinvention will be described with reference to FIG. 5.

In the third embodiment described above, the power modules are welded tothe circuit case 5, but in the present fourth embodiment, the powermodules are welded to a cooling case 7A.

The cooling case 7A in the present embodiment is formed with openingspenetrating into the cooling liquid chamber 11 and matching the modulebase plates 2 in size. The module base plates 2 are placed into theopenings in the cooling case 7A, and the edges of the openings and themodule base plates 2 are joined to each other by welding without a gapbetween them. The cooling case 7A is fixed with bolts 10 to the circuitcase 5 from outside it so that the power modules are positioned withinthe circuit case 5 through a circuit case opening 6. Between bothmembers, a sealing member 8, such as an O ring, is inserted all aroundtheir joining portion (the whole circumference of the circuit caseopening 6).

Also in the present structure, as in the foregoing embodiments, when thecooling liquid 12 passes through the cooling liquid chamber 11, it canefficiently cool the back faces 15 of the module base plates. Since themodule base plates 2 and the cooling case 7A are fixed to each other bywelding, the quality of their joining portions is not subject todeterioration due to aging. Therefore, there is no possibility for thecooling liquid to pass the welded portions 4 and leak into the circuitcase 5, and high reliability can be obtained. Even if the quality of thesealing member 8 deteriorates over time and allows the cooling liquid toleak, the cooling liquid 12 will merely leak out through the gap 16between the cooling case 7 and the circuit case 5, but never into thecircuit case 5.

Furthermore, as the power modules are welded directly to the coolingcase 7 in the present embodiment, the module supporting plate 3 and someof the sealing members 8 in the first embodiment can be dispensed with,and it is possible to restrain manufacturing cost. Moreover, becauseseal portions to be sealed by sealing members are reduced in number,reliability against cooling liquid leakage can be enhanced.

While the module base plates 2 are directly welded to the edges of theopenings in the cooling case 7A in the present embodiment, it is alsopermissible to weld the module base plates 2 to the module supportingplates 3 and weld the module supporting plates 3 to the edges of theopenings in the cooling case 7A like the first embodiment.

A fifth embodiment of the liquid-cooled circuit device of the presentinvention will be described with reference to FIG. 6.

This embodiment uses a circuit case 5A in which the circuit case and thecooling case in the foregoing embodiments are integrated with eachother. Part of the circuit case 5A is recessed from inside towardoutside to form a cooling liquid chamber 11. To the opening 6 of therecess, the module supporting plate 3 mounted with power modules isjoined by welding without a gap between them so that the power circuitelements 1 are positioned on the reverse side to the cooling liquidchamber 11. The inside of the circuit case 5A is divided into twochambers by the module supporting plate 3. One of the two chambersconstitutes the cooling liquid chamber 11 mentioned above, and theother, a circuit accommodating chamber 13. The cooling liquid chamber 11is provided with an inlet and an outlet for the cooling liquid, thoughnot shown.

Because the cooling liquid chamber 11 is completely sealed in thepresent embodiment, the problem of possible cooling liquid leakage canbe avoided. Moreover, since no sealing member whatsoever, such as an Oring, is used, the structure is extremely simplified, and it is possibleto suppress manufacturing cost.

Next, a sixth embodiment of the liquid-cooled circuit device of thepresent invention will be described with reference to FIG. 7.

The sixth embodiment is a variation of the fifth embodiment, and thesize of the openings 6 penetrating from the circuit accommodatingchamber 13 to the cooling liquid chamber 11 is matched with the size ofthe module base plates 2. The module base plates 2 are placed in theopenings 6, and the edges of the openings 6 and the module base plates 2are joined to each other by welding without a gap between them. In otherwords, in the present embodiment, the module supporting plate 3 in thefifth embodiment is dispensed with, and the module base plates 2 aredirectly welded to part of the inner face of the circuit case 5A.

Since the present embodiment differs from the fifth embodiment basicallyonly in the presence or absence of the module supporting plate 9, it canprovide the same advantages as the fourth embodiment except that themodule supporting plate 9 can be dispensed with.

Next, a seventh embodiment of the liquid-cooled circuit device of thepresent invention will be described with reference to FIG. 8.

The present embodiment is a variation of the sixth embodiment, and acircuit case 5B is divided into two parts. The present embodiment isbasically similar to the fifth embodiment in all other respects. Thecircuit case 5B in the present embodiment comprises a cooling chamberside part 7B and the remaining part. The cooling chamber side part 7Bcomprises a part forming a recess to constitute the cooling liquidchamber 11 and a wall part continuous to an opening edge of the recess.The wall part and a part forming the circuit case 5B together with thewall part are connected with bolts 10, and between them is provided an Oring as the sealing member 8.

Though this bisecting of the circuit case 5B results in an increasednumber of parts, it facilitates the welding of power modules to thecooling chamber side part 7B, and the wiring, repair, maintenance andinspection within the circuit case 5B.

Next, an eighth embodiment of the liquid-cooled circuit device of thepresent invention will be described with reference to FIG. 9.

The present embodiment is a variation of the fifth embodiment, and it isbasically similar except that a cooling liquid case is bisected. Thecircuit case 5C in the present embodiment comprises a side wall portionfor forming the cooling liquid chamber 11 together with a bottom wall 7Cand a remainder portion for forming the module accommodating chamber.The bottom wall 7C is fixed to the side wall portion with bolts 10, andbetween them is provided an O ring as the sealing member 8.

With this structure, it is possible to easily perform the welding of themodule supporting plate 3 to the circuit case 5C, and the repair,maintenance and inspection within the cooling liquid chamber 11.

To add, it should be noted that the first through fourth embodiments ofthe invention described above are also the same kind as the seventh andeighth embodiments in which the circuit case and the cooling case areformed from two parts.

Next, a ninth embodiment of the liquid-cooled circuit device of thepresent invention will be described with reference to FIG. 10.

The present embodiment is a variation of the sixth embodiment, and achannel for the cooling liquid 12 is formed so that the cooling liquid12 comes into contact with the respective power modules in series. Thepresent embodiment is basically similar to the sixth embodiment in allother respects. Part of the wall of the circuit case 5Aa is recessed ina U shape, and the recessed part constitutes a cooling liquid chamber11A.

The width of openings 6 of the cooling liquid chamber 11A issubstantially the same as that of the module base plates 2. The modulebase plates 2 are fitted into the openings 6, and joined to edges of theopenings 6 without a gap between them. One end 11 a of the U-shapedcooling liquid chamber 11A is connected to an inlet of cooling liquid,and the other end 11 b is connected to an cooling liquid discharge port.

By narrowing the width of the cooling liquid chamber 11A as describedabove and thereby narrowing a sectional area of the channel for thecooling liquid 12, the flow rate of the cooling liquid 12 can beincreased, and the performance of cooling the power modules can beenhanced eventually.

To add, the shape of the cooling liquid chamber 11A in the presentembodiment can obviously be applied not only to the sixth embodiment butalso to any other embodiments.

Next, a tenth embodiment of the liquid-cooled circuit device of thepresent invention will be described with reference to FIG. 11.

The present embodiment invention is a variation of the first embodiment,and nozzles 23 for spraying cooling liquid 12 substantially vertical tothe back faces 15 a and 15 b of the module base plates 2 are formedwithin the cooling liquid chamber 11. Its configuration is basically thesame as that of the first embodiment in all other respects.

Cooling water discharge ports for discharging cooling water from thecooling water chamber 11, though not shown, are respectively providedfor module base plates 2 just like the nozzles 23, and the configurationis so designed that the cooling liquid ejected from the nozzle 23 maynot interfere with the cooling liquid having come into contact with theback face 15 of the module base plate 2.

To add, the shape of the cooling liquid chamber in the presentembodiment of the invention can obviously be applied not only to thefirst embodiment but also to any other embodiments.

Next, an eleventh embodiment of the liquid-cooled circuit device of thepresent invention will be described with reference to FIG. 12.

The present embodiment is also another variation of the firstembodiment, and pluralities of heat radiation fins are formed on theback faces 15 of the module base plates 2. The formation of such heatradiation fins expands an area of contact with cooling liquid 12 and canthereby enhance the efficiency of cooling the power modules.

Although, in the present embodiment, parallel type heat radiation finsare used, fins of some other type can be used as well. The heatradiation fins described in connection with the present embodiment canobviously be applied not only to the first embodiment but also to anyother embodiments.

According to the invention, the module base plates and the matingmembers to be joined thereto are welded together. Therefore, it ispossible to prevent the cooling liquid from infiltrating between them,and there is no need to provide portions for mounting O-rings, screwsand the like to the module base plates, so that it is possible to reducethe size of the module base plates. As a result, the manufacturing costcan be reduced, and the overall size of the device can be reduced.

Furthermore, where a friction stir welding method is used for theabove-described welding, the thermal impact on the circuit elementsduring the welding process can be minimized. A liquid-cooled circuitdevice comprising: a module having a circuit element and a module baseplate on surface of which the circuit element is mounted; a circuit casefor accommodating said module; and a cooling liquid chamber for flowinga cooling liquid in contact with a back face of said module base plateof said module, wherein said module base plate of said module is fittedinto an opening provided in a member forming said cooling liquid chamberand welded without a gap.

It should be further understood by those skilled in the art that theforegoing description has been made on embodiments of the invention andthat various changes and modifications may be made in the inventionwithout departing from the spirit of the invention and the scope of theappended claims.

What is claimed is:
 1. A method for manufacturing a circuit device inwhich circuit elements are mounted on base plates and the base platesare fixed to other members of the circuit device, wherein said baseplates and said other members are joined to each other by welding, usinga friction stir welding method utilizing a plastic flow due to frictionheat generated by rotation of a rotary tool.
 2. The method formanufacturing a circuit device as claimed in claim 1, wherein all ofsaid base plates and said other members contain the same metallicelement.